Leaves

Leaves

- lateral outgrowth of the stem

- flattened,expanded

- leaf primordia

- leaf buttress

Leaf Parts:

1. Petiole

- cylindrical part

- attaches blade to the stem

2. Lamina or Blade

- flattened green

part

Petiolated

Sessile or apetiolated

Monocot leaf

• Supported by leaf sheath• Ligules and auricles Functions: 1. protection from dirt water

3. Stipule

- two leaflike flaps of the petiole

- dicot leaves

a. Stipulate – w/ stipule

b. Exstipulate – without

4. Midrib

- central vein

5. Veins

- conducting tissue of the leaf

6. Veinlets

- secondary veins

7. Margin

- edge of the leaf

Simple leaf - one blade or lamina

Compound leaf - blade is divided into two or

more leaflets or (pinnae) - petiolule Rachis – continuation of the

petiole where the leaflets are attached

Types of Compound Leaves

A. Pinnately Compound

- leaflets are arranged laterally along the rachis (featherlike fashion)

1. Simple Pinnate

a. Even pinnate

- each leaflet has a pair

b. Odd pinnate

- terminal leaflet has no

pair

2. Bipinnate

- primary rachis branches

into secondary rachis that

bears the leaflets

3. Tripinnate

- with primary, secondary

and tertiary rachises

B. Palmately Compound

- leaflets radiate from a

common point

1. Unifoliate

- single leaflet at the

tip of the stalk

2. Bifoliate

3. Trifoliate

4. quadrifoliate

PHYLLOTAXY

Phyllotaxy

1. Alternate - one leaf at each node 2. Opposite - two leaves opposite

each other at each node

3. Whorled/verticillate - several leaves at equal

distance around the node

4. Spiral - leaves arise

succeedingly around the stem

5. Decussate - two opposite leaves at right angles to the

one below or above it

Shape

Margin

Leaf Venation

2 Systems of Venation:

1. Reticulated/Netted

- main vein branches

- forms network

a. Pinnately netted

- main vein

- veins and veinlets

arise from the

midrib and ramify

throughout the lamina

b. Palmately netted

- principal veins arise at

one point at the base of

the leaf

c. Radiately netted

- principal veins radiate

at the tip of the petiole

Colocasiaesculenta (gabi)

2. Parallel/Striate Venation

- veins are parallel with the midrib

- common in monocots

a. Radial Parallel

- parallel veins form

acute/right angles to

the midrib

Diagram of Dicot Leaf

Dicot Leaf Cross section

1. Epidermis

- upper and lower

- single layer of cells

- derived from protoderm

Functions:

a. Protects leaf from dessication –(cuticle)

b. Abrasion

c. Prevents entry of fungi and bacteria

d. Regulates exchange of gases (Oxygen and carbon dioxide

1. Trichomes - protection against water

loss 2. Stomata - more stomata in lower

epidermis - high temperatures - high concentration of CO2

close stomata

2. Mesophyll

- located between the upper and lower

epidermis

- dicots (2 distinct layers)

a. Palisade mesophyll

- arranged in compact columnar fashion

- most photosynthetic activity takes

place

b. Spongy mesophyll

- irregularly shaped

- prominent intercellular air spaces

- diffussion of carbon dioxide to other

parts of leaf

3. Vascular bundle/Leaf Vein

3. xylem

- part that faces upper

surface of the leaf

phloem

- part that faces the lower surface of the leaf

bundle sheath cells

- for added strength and protection

Diagram of Monocot Leaf

Monocot leaf cross section

Internal Anatomy of Monocot Leaf 1. Upper epidermis

- covered with cuticle

- bulliform cells

- stomata present in upper and lower epidermis

Guard cells monocot

- dumbbell in shape

Guard cells dicot

- kidney shaped

2. Mesophyll

- not differentiated into palisade and spongy mesophyll

Pine leaf cross sectionCuticle - much thicker Epidermis - multilayeredMesophyll

Modified Leaves

Spines - modified leaves or

modified stipules - for protection

Tendrils - slender, coiling

structures - for support - exhibit thigmotropism (opposite side begins to

grow rapidly )

b

Bracts - modified leaves at the

base of the flowers - colored bracts for

attraction ex. Poinsettia bougainvilla

Uncutiniced leaves - for absorption ex. Digman

Expanded leaf like petiole - for additional

photosynthesis ex. Pomelo

Fleshy and succulent leaves - for storage ex. Sabila

Plantlets at the tip of the leaves

- for reproduction

ex. kalanchoe

Insectivorous leaf - for absorption